In a typical inkjet recording or printing system, ink droplets are ejected from a nozzle at high speed toward a recording element or medium to produce an image on the medium. The ink droplets, or recording liquid, generally comprise a recording agent, such as a dye or pigment, and a large amount of solvent in order to prevent clogging of the nozzle. The solvent, or carrier liquid, typically is made up of water, an organic material such as monohydric alcohol, a polyhydric alcohol, or mixtures thereof.
Inks used in various inkjet printers can be classified as either dye-based or pigment-based. In dye-based inks, the colorant is molecularly dispersed or solvated by a carrier medium. In pigment-based inks, the colorant exists as discrete particles. It is known that pigment-based inks perform better than dye-based inks with respect to stability properties such as light fade or ozone fade.
An inkjet recording element typically comprises a support having above, not necessarily adjacent, at least one surface thereof an ink-receiving or image-forming layer. The ink-receiving layer can be either porous or swellable.
In general, porous inkjet receivers absorb ink much faster than swellable inkjet receivers. This allows handling of the print sooner and the propensity of image artifacts such as coalescence are reduced. There are many porous inkjet receivers available today. They include porous glossy receivers comprised of small (<200 nm) inorganic particles and binder, which is usually an organic polymer. The polymeric binder can be hydrophilic in nature, for example poly(vinyl alcohol), hydroxypropyl cellulose, hydroxypropyl methyl cellulose, a poly(alkylene oxide), poly(vinyl pyrrolidinone), poly(vinyl acetate) or copolymers thereof, or gelatin. The polymeric binder may also be hydrophobic in nature. Examples of hydrophobic binders include poly(styrene-co-butadiene), a polyurethane latex, a polyester latex, poly(n-butyl acrylate), poly(n-butyl methacrylate), poly(2-ethylhexyl acrylate), a copolymer of n-butylacrylate and ethylacrylate or a copolymer of vinylacetate and n-butylacrylate.
For these porous glossy receivers, the typical weight ratio of inorganic particles to organic binder ranges from 75:25 to 95:5. There has to be enough binder present to adhere the inorganic particles together and provide integrity of the layer. If too much binder is present, however, porosity or void volume of the layer is reduced, resulting in slower drying rates and increased propensity for image artifacts.
It has been found that when these porous glossy receivers are printed with pigmented inks, very little dot spread occurs as a result of the ink droplet hitting the receiver surface. Although this is desirable, to some extent, from an image sharpness standpoint, it may be undesirable for printing efficiency and print density. When an ink drop hits the receiver surface and can spread, it increases the ink covering power resulting in higher densities.
U.S. Pat. Nos. 6,399,159 and 6,565,930 discuss the use of plasma treatment of paper and polyolefin imaging supports for obtaining the proper surface characteristics to promote adhesion of photosensitive coating materials, image forming layers, non-photosensitive polymeric coatings or laminates, and/or layers typically coated thereon. However, there is no teaching of plasma treatment directly to the surface ink-receiving layer for inkjet applications.
U.S. Pat. No. 5,605,750 discloses an opaque recording for use in an inkjet printer comprising a lower layer of a solvent-absorbing microporous material and an upper image-forming layer of porous pseudo-boehmite. A corona-discharge treatment may be applied to the lower microporous material layer before application of the upper image-forming layer for improved adhesion of the layer. However, there is no mention of plasma treatment to the uppermost surface layer for enhanced dot spread.
It is the object of this invention to provide an inkjet receiving element that has increased dot spread and printing density when printed with pigmented ink.